The Use of Semi-solid Agar for the Detection of Bacterial Motility

Abstract

Semi-solid agar (nutrient broth plus 0.5% agar) for detecting bacterial motility was studied with 1,051 cultures, representing over 60 spp., and the results compared with those of the hanging-drop technique. The agar medium in tubes was inoculated by the stab method. Motility is manifested macroscopically by a diffuse zone of growth. After incubation for 1 day, the agar method gave results practically identical with those of the hanging-drop, but after 2 days it showed 4% more positive cultures. The semi-solid agar method is particularly advantageous in teaching schedules and routine testing because the results are cumulative and macroscopic.